The invention relates to an internal combustion engine with a first and a second injector for injecting fuel directly into a combustion chamber in a cylinder in a crankcase of the internal combustion engine and to a method for operating the internal combustion engine.
The variation of the injection quantity of a direct-injection fuel injector from the minimum to the maximum load on the internal combustion engine, the variation being engine-speed and load dependent as is required, impairs precise control of small and very small fuel injection quantities. The maximum fuel quantity required likewise determines the size or diameter of the injection holes in the injector tip and compromises the achievable droplet spectra (shifting of the droplet diameter in the direction of larger droplets) at small and very small loads on the internal combustion engine. Moreover, the large droplets lead to a large penetration depth of the fuel jet into the combustion chamber and to wetting of other components in the combustion chamber. As a result of these factors, the fuel pressure must be increased, with disadvantages in terms of outlay on construction and friction. Moreover, not all of the problems mentioned can be fully solved with the conventional increase in fuel pressure.
The use of another method of supplying fuel mitigates both problems. The use of intake manifold injection, for example, is known in this context. The disadvantage here is the lack of internal cooling of the combustion chamber by the directly injected fuel, resulting in a reduction in compression.
To improve mixture preparation of an internal combustion engine, German patent application DE 10 2004 034 505 A1 discloses, for example, the use of two fuel injectors for injecting the fuel. DE 10 2004 034 505 A1 proposes inserting a fuel injector into the intake pipe and using a fuel injector for direct injection of the fuel into the combustion chamber.
German Patent DE 10 2006 014 071 B3, which the present invention considers a starting point, furthermore discloses a combustion method for an internal combustion engine in which fuel is injected directly into the combustion chamber by one or more injection devices. Here, the injection process is divided into at least two partial injections, which take place in different areas of the combustion chamber. In DE 10 2006 014 071 B3, it is proposed that a pilot injection be directed into central areas and a main injection into outer areas of the combustion chamber, with free spatial arrangement of the injection jets.
Even if this prior art does not have any disadvantages in principle, it is the underlying object of the present invention to improve the metering accuracy of fuel for an internal combustion engine of the type in question.
This and other objects are achieved by providing an internal combustion engine, and method of operating same, with a first injector and a second injector for injecting fuel directly into a combustion chamber in a cylinder in a crankcase of the internal combustion engine. The combustion chamber is delimited on one side by a piston arranged in the cylinder in such a way that it can perform a stroke motion and on the other side by a cylinder head. At least one gas exchange inlet valve and one gas exchange outlet valve are provided in the cylinder head for a charge exchange, wherein the first injector is arranged so as to be largely oriented in the direction of a cylinder axis, and the second injector is arranged so as to be oriented at an angle to the cylinder axis. A maximum of 80% of a full-load fuel quantity required by the internal combustion engine for a full load can be introduced into the cylinder using the first injector and a maximum of 50% of said quantity can be introduced using the second injector.
In addition to the solution of the above-mentioned problems, there is further functional potential through appropriate configuration of the fuel injection quantities of the individual injectors and, if appropriate, of other mixture preparation characteristics, e.g. modifying the jet pattern, provision of the minimum quantity of fuel, specialization on a particular load range of the internal combustion engine. Owing to the capacity, according to the invention, for adapting the fuel flow rate through the injector, the internal friction in the high-pressure pump can be reduced, especially at low loads on the internal combustion engine.
In a preferred embodiment, the first and the second injectors can be operated simultaneously and/or with a timed offset. This allows further adaption to different operating states of the internal combustion engine.
In a preferred method of operating the internal combustion engine, the fuel injection of an idling fuel quantity is performed only with the first injector when the internal combustion engine is idling.
In a further preferred embodiment, the fuel injection of a fuel quantity for catalyst heating is performed only with the first injector during catalyst heating.
It is further advantageous to have fuel injection of between 50% and 90% of a part-load fuel quantity performed with the first injector and between 10% and 50% of the quantity performed with the second injector during a part load on the internal combustion engine. It is also preferred to have fuel injection of between 50% and 80% of a full-load fuel quantity performed with the first injector and between 20% and 50% of the quantity be performed with the second injector during a full load on the internal combustion engine.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.